The invention relates to an analysis system for the analysis of a sample, comprising a gel permeation chromatograph that is coupled with a nuclear magnetic resonance (=NMR) spectrometer, wherein the chromatograph has a gel permeation chromatography (=GPC) separating column that is filled with porous particles.
Such an analysis system is described, for example, in A. Nordon at al., Analyst (2001), No. 126, pp. 260-272.
The analysis and monitoring of the polymer quality, particularly with respect to molecule size, chain length distribution, molecular linking, and chemical composition is a basic requirement for the development and production of powerful polymers, composite materials containing polymers and macromolecules. Measuring methods are used in the monitoring of the polymer quality that must be both selective with respect to molecular size and sensitive to the chemical composition.
The measuring methods for monitoring polymer quality are largely based on liquid-chromatography separation methods, in particular, gel permeation chromatography (=GPC), also called size exclusion chromatography (=SEC) or GPC/SEC. The substance to be examined (usually a mixture of macromolecules of different sizes) is dissolved in an eluent (eluting agent) and passes through a separating column that contains a stationary phase; the stationary phase delays the progress of the various macromolecules in the sample for different lengths of time. In GPC, the macromolecules contained in the sample are separated according to size (hydrodynamic radius). In this case, the separation effect of GPC is based on entropic interaction with the stationary phase and therefore provides no information about the chemical composition of the macromolecules. In other chromatography methods such as high performance liquid chromatography (=HPLC), on the other hand, the separation effect is based on enthalpic interaction.
The actual chemical analysis of the sample can be performed with one of the spectrometers placed downstream of the chromatographic separation. Isolated spectrometers would only provide averaged information about the chemical composition of the molecular blend contained in the sample; information about individual fractions of the molecular blend can only be derived after upstream separation.
Currently, mainly ultraviolet (=UV) spectrometers and infrared (=IR) spectrometers are used in conjunction with GPC. UV and IR spectrometers are attractively priced but their measurement capability is limited for physical reasons, so that both the qualitative and quantitative information they can provide about the chemical composition of the sample both is rather limited.
Currently, the most powerful method of chemical analysis of samples containing polymers in general use is high-resolution, high field NMR spectroscopy using superconducting magnets (corresponding to a proton frequency of typically 500 MHz or more). High-field NMR spectroscopy, usually implemented as FT-NMR, is currently the most versatile and precise method of identifying chemical substances. However, even with high-field NMR spectroscopy, complete chemical deformulation of all components of a sample containing a polymer blend can only be achieved with upstream separation.
The coupling of GPC and high-field NMR is, for example, summarized in a review by T. Kitayama, K. Ute, “On-line SEC-NMR,” in “Modern Magnetic Resonance,” pp. 395-401, edited by G. A. Webb, 2006.
However, the use of high-field NMR spectroscopy coupled with GPC requires a very large investment in apparatus. The high-field NMR spectrometer used for the qualitative and quantitative chemical analysis of fractions is very expensive to procure and maintain, in particular, due to the use of superconducting magnet coils, which are difficult to manufacture and usually large and heavy, and the need to cool them with expensive liquid helium during operation. The handling of cryogenic liquids and the complex measuring methods and complicated operation also mean they are difficult and expensive to operate.
Where individual quality control and process monitoring tasks have to be performed, low-field NMR spectrometers are often used. Commercially available low-field NMR devices such as “the minispec” from Bruker Optics GmbH, Ettlingen, Germany, are based on permanent magnet systems and are considerably smaller and more economical than high-field NMR devices. However, as a rule, they only allow little to no dispersion, so that chemical differentiation and identification of the components of samples by means of chemical shift is hardly possible.
A. Nordon et al., Analyst (2001), No. 126, pp 260-272, in their review describe the possibilities of low-field NMR in online use. This is where the reference to spectroscopic measurements in the low field is also to be found. In the summary, it is also pointed out that methods of high-field NMR, as are used, for example, at 500 MHz in conjunction with GPC coupling, could be of interest for online NMR analysis.
The coupling of HPLC and NMR in the laboratory is also known; see, for example, K. Albert J. Chromatography A, No. 703 (1995), pp. 123-147. Here, electromagnets for field generation are used, cf. N. Watanabe, E. Niki, Proc. Japan. Acad. 54, Ser. B, 194 (1978), or also E. Bayer et al., J. Chromatography 186, pp. 497-507 (1979).
The object of this invention is to provide an analysis system with which quantitative and qualitative chemical analysis of samples containing substances of different molecular sizes can be performed with less expensive apparatus.